Reflection measurements of test objects are carried out, for example, to determine the wall thickness of the test objects. Compared to transmission measurements, reflection measurements have the advantage that the test object has to be accessible only on one side. However, a disadvantage of reflection measurements is the small signal-to-noise ratio, since for measurements of test objects made of plastics, for example, the reflectance is lower than the transmittance.
To obtain the highest possible signal quality of the measured radiation, the receiver is separate from the transmitter. For example, a measuring device for reflection measuring measurements is known from US 2004/095147 A1, in which a dielectric body is situated between a terahertz transmitter and the test object, and between the test object and a terahertz receiver, to improve the signal quality. A disadvantage of the known measuring device is that it has a less flexible and complicated design.